Republican Rep. Denny Rehberg&rsquo;s decision to challenge Democratic Sen. Jon Tester makes this Montana race one of the most competitive in the country. Because of that, Roll Call Politics has moved the race rating from Leans Democratic to Tossup.

Rehberg will announce his plans Saturday, as Roll Call first reported, and the GOP primary field is expected to clear for him. The race promises to heat up over the next 21 months, with internal Rehberg polling numbers obtained by Roll Call showing that the race is already tight.

A Tester spokesman said in a statement Tuesday that the Senator looks forward to beginning an honest debate following the June 5, 2012, primary. Not all Montana Democrats are waiting to pounce: The state party released a scathing statement regarding Rehberg just an hour after his plans were reported.

Rehberg lost his first Senate bid in 1996 to Democratic Sen. Max Baucus. Since Rehberg was first elected to the House in 2000, he has never won with less than 59 percent of the vote.

Although Montana leans Republican, it has two Democratic Senators and a Democratic governor, and Barack Obama lost there by just 3 percentage points in the 2008 presidential election.

According to financial reports due Monday, Tester and Rehberg are even in cash on hand. Tester reported having $562,000 in the bank as of Jan. 1, while Rehberg had $553,000.